1) I think you mean main gear (big gear, right). It is 0.8 and in the kit include 6 gears (3 1st speed and 3 2nd speed) so you can get the right ratio for the track
2) I am not sure if the kyosho one fit. But the kit comes with carbon fiber shock towers (front and rear) already so you do not need to upgrade
3) 3d with lightened flywheel
4) You can adjust the wheel base and height of the rear hub. And it comes with 2 sets of inserts for fine tuning.
It is a good car for the price and I like it more than my 3R as the rear is more stable.